Annulate lamellae (AL) are a membranous structure frequently observed in differentiating gametes and tumor cells. In spite of numerous morphological studies, the function and biochemical composition of this membrane system are not well understood. In this study, we have examined the AL membrane system of vinblastine-treated mouse L cells using immunocytochemistry and Western blot analysis. Our results show that antibodies directed against nuclear envelope lamins, i.e., lamins A, B, and C, did not cross react with constituents of the AL membrane system. Furthermore an AL-specific antibody failed to react with the nuclear envelope and reacted minimally producing only a background stain over other cellular components. The data suggest that the AL membrane system has a distinct molecular make-up that is antigenically distinct from that of other subcellular structures.

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